The invention concerns a cooling device comprising a cryostat and a cold head, in particular the cold head of a pulse tube cooler, the cryostat comprising                a vacuum container with a vacuum container wall, wherein the vacuum container wall seals off a vacuum inside the vacuum container from the environment,        and a cryocontainer for a cryogenic liquid and/or a cryogenic gas, having a cryocontainer wall, wherein the cryocontainer is arranged inside the vacuum container and the cryocontainer wall seals off the inside of the cryocontainer from the vacuum of the vacuum container, wherein a room temperature part of the cold head is mounted in a vibration-damped fashion to the vacuum container wall by means of decoupling elements and a cooling arm of the cold head projects into an access opening of the cryostat to the cryocontainer along a longitudinal axis, and wherein a flexible sealing section is provided which connects the vacuum container wall directly or indirectly to the room temperature part of the cold head.        
A cooling device of this type is disclosed in U.S. Pat. No. 7,287,387 B2.
Nuclear magnetic resonance (NMR) apparatus, in particular NMR spectrometers and NMR tomographs, require strong magnetic fields which are often generated by means of superconducting magnet coils. The superconducting magnet coils must be operated at a cryogenic temperature. For this reason, the magnet coils are typically arranged in the cryotank of a cryostat which is filled with a cryogenic liquid, e.g. liquid helium. In order to maintain the operating temperature on a long-term basis and at the same time minimize the consumption of cryogenic liquids, the cooling arm of a cold head projects into the cryotank which withdraws heat. The cryotank is surrounded by a vacuum tank for thermal insulation.
NMR measurements can be disturbed by mechanical vibrations of the NMR apparatus which are introduced, in particular, via the cold head mounted to the cryostat.
In case of cooling in accordance with the pulse tube cooling principle which is often applied, periodic pressure fluctuations of a working gas are established in the cold head. For this purpose, a control valve alternately connects a high-pressure reservoir and a low-pressure reservoir of the working gas to the cold head. The change-over frequency of the control valve is typically approximately 1 to 2 Hz. Disturbing vibrations at the cold head also occur with other cooling principles (e.g. Stirling, Gifford-McMahon).
EP 0 780 698 A1 describes an NMR device with mechanical decoupling between a cooling means and a cryotank.
U.S. Pat. No. 7,287,387 B2 discloses an apparatus for cooling superconducting magnets, wherein a two-stage cold head projects into an inner chamber which is filled with helium and is surrounded by a vacuum chamber. The room temperature part of the cold head is mounted to a cold head flange which is mounted to the vacuum chamber via springs. For sealing off the vacuum tank from the environment, a bellows is arranged between the cold head flange and the outer wall of the vacuum chamber. Bellows are also provided for connecting the cold head flange to the wall of the inner chamber in order to seal the vacuum tank with respect to the inner chamber. The oscillating mounting of the cold head on the springs minimizes introduction of vibrations to the vacuum chamber due to fastening of the cold head on the vacuum chamber. However, the unilaterally pressurized bellows, which are used for sealing the vacuum chamber and the inner chamber, still cause non-negligible mechanical coupling between the cold head and the vacuum chamber and between the cold head and the inner chamber.
U.S. Pat. No. 5,018,359 discloses a cryogenic cooling apparatus, in which a cold head is mounted to a magnetic shield and one cooling arm of the cold head projects into a vacuum container, wherein the cooling stages are coupled to two radiation shields. A bellows is used between a flange at the cold head and an outer wall of the vacuum container for sealing off the vacuum from the environment. Also in this case, the unilaterally pressurized bellows causes non-negligible mechanical coupling with the cold head.
DE 10 2004 034 729 B4 discloses a cryostat configuration, wherein a cold head is mounted via springs to the outer wall of the cryostat. One cooling arm of the cold head projects into a neck tube of a helium container. In order to establish thermal coupling between an upper cooling stage of the cooling arm and a radiation shield, finned coupling surfaces are provided between which a gas gap remains.
It is the underlying purpose of the invention to present a cooling device, in which mechanical coupling between the cold head and the cryostat is further reduced, in particular, in order to enable performance of NMR measurements with fewer disturbances caused by external vibrations.